1. Field of the Invention
This invention generally relates to a sheet member, a manufacturing method of the sheet member and an exhaust gas processing device in which the sheet member is provided as a holding sealer.
2. Description of the Related Art
So far, many various kinds of exhaust gas processing devices have been suggested, and these have been used practically. A typical exhaust gas processing device has a casing made of a metal shell on a exhaust pipe connected to a exhaust gas manifold of an engine, in which casing an exhaust gas processing body having lots of cells divided by cell walls is arranged thereon. Typically, these cells are constructed in a honeycomb structure. Especially, in this case, the exhaust gas processing body is called a honeycomb structure. As an example of the exhaust gas processing body, there are a catalyst carrier and a filter for exhaust gas like a diesel particulate filter (DPF). For example, in the case of a DPF, particles (particulate matter) are trapped by cell walls during the exhaust gas passing through the exhaust gas processing body via each cell based on the above structure; thereby particles can be removed from the exhaust gas.
In general, in the case of manufacturing the exhaust gas processing device, a holding sealer comprising inorganic fibers is provided. In order to prevent damage due to direct contact between the exhaust gas processing body and an inner surface of the casing during driving the vehicle and also to prevent leakage of the exhaust gas from a space gap between the casing and the exhaust gas processing body, the holding sealer is used. In addition, the holding sealer has an important role to prevent the exhaust gas processing body falling off due to exhaust pressure of the exhaust gas. Moreover, the holding sealer has an important role in maintaining the exhaust gas processing body at a required high temperature for ensuring its reactivity.
Classifying roughly, there are two kinds of methods for manufacturing such a holding sealer; one is a needling process and the other is a papermaking process. As described in patent document 1, for example, the needling process is such that inter-woven means for fibers like needles are stuck into the laminated mat and pulled off from the laminated mat, and thereby the holding sealer is manufactured. Also, the papermaking process is usually called a wet process, and is a processing method to form the holding sealer via the processes of an open fiber, a formation of slurry, a molding and a compression drying. This method is described in patent document 2.    Patent Document 1: JP 2000-344583    Patent Document 2: JP 2003-293757